1. Field of Invention
The present invention relates to a tensioner, and more particularly to a it tensioner applied in power or transmission devices.
2. Description of Related Art
A tensioner is usually applied to a member in a power or transmission system, such as an endless flexible member for transmitting the power of a shaft in a power system. In order to transmit power smoothly and prevent vibration caused by change of tension of the endless flexible member, the tensioner is usually installed on the loose side of the endless flexible member to adjust tension of the endless flexible member automatically.
Please refer to FIG. 1, which is a cross section view showing a conventional tensioner. The tensioner 100 includes a base 102, a piston 104, a rack 106, a ratchet 108, a spring 110, a spring 112, and a pin (not shown). The rack 106 is disposed on the side wall of the piston 104 along a direction parallel to the central axis thereof. The spring 110 and the piston 104 are disposed in a recess portion of the base 102. The ratchet 108 is pivotally connected to the base 102 so that the lower portion of the ratchet 108 can mesh with a tooth of the rack 106. The ending of the pivoting shaft of the ratchet 108 is connected to a plate 114 disposed and extending on the surface of base 102. The plate 114 includes a through hole 116. A fastening hole (not shown) is disposed on a location of the base 102 corresponding to the location of the through hole 116.
When the manufacture of the tensioner 100 is completed in a factory, the pin of the tensioner 100 passes through the through hole 116 and stays in the fastening hole of the base 102 corresponding to the through hole 116. At this time, the ratchet 108 cannot rotate around the pivoting shaft, and the lower portion of the ratchet 108 meshes with a tooth of the rack 106, and the piston 104 stays in the recess portion of the base 102 and in a static state. This arrangement can make the piston 104 temporarily stay in the recess portion of the base 102, and can prevent the piston 104 from separating from the recess portion of the base 102. When the tensioner 100 is being assembled, the tensioner 100 is first placed in a predetermined location, and then the pin is pulled out so that the piston 104 is pushed away from the recess portion of the base 102 by springback force of the spring 110. When the piston 104 contacts the device, such as the endless flexible member, in order to control the tension of the device, the springback force for pushing the piston 104 will be offset by the tension of the device and stays in an equilibrium state. When the device is in operation, the variations of the tension of the device will push the piston 104 to move slightly such that the variations will be balanced automatically.
When the device is in repair or adjustment, if the piston 104 of the tensioner 100 is in need of staying at the original location set by a factory or being pushed back into the recess portion of the base 102, the upper portion of the ratchet 108 is pushed to be without mesh engagement with a tooth of the rack 106 and then the piston 104 is pushed back into the base 102. Thereafter, a specific pin, i.e. the pin including a diameter fitting with the diameter of the through hole 116 in the plate, is used to fix the piston 104. This structure is inconvenient for operators' manipulation. When the operation is improper, the piston 104 will be rapidly pushed along the direction away from the base 102 due to springback force of the spring 110, which, in turn, makes the operators get injured or damages some goods.
Hence, there is a need to provide a novel tensioner for improving convenience and safety in operation.